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Field_Overlap_Start, Field_Overlap_End

Obsolete

Overlap columns were replaced by multi-segment relationships in DataFlex 11.0 and are now considered obsolete.

Supported By

  • SQL Drivers (SQL Server, DB2, and ODBC)

Value

  • 1 .. Number of columns in the table

Associated Attributes

Description

The Field_Overlap_Start and Field_Overlap_End keywords are used to define an overlap column. An overlap column is a logical column that “overlaps” multiple underlying real columns. The keywords are set to the numbers of the columns that are overlapped.

For example, if we want to define a column at number 5 called My_Overlap starting at column 3 and ending at column 4 (inclusive), we need to place the following lines in the intermediate file:

Field_Number        5
Field_Name          My_Overlap
Field_Overlap_Start 3
Field_Overlap_End   4

The lines above will insert a column in the table definition. Column number 5 is a logical column; the original column number 5 and higher will shift one position. Overlaps defined in this way always overlap complete columns.

Please note that the overlap column will be inserted when the column definition is finished at a new field group header, an index group header, or the end of the intermediate file. Therefore, the following intermediate file definition will generate two subsequent overlap columns at positions 5 and 6. The original column number 5 and higher will have shifted two positions.

Field_Number        5
Field_Name          Eventually_Field_6
Field_Overlap_Start 2
Field_Overlap_End   3
Field_Number        5
Field_Name          Eventually_Field_5
Field_Overlap_Start 1
Field_Overlap_End   3

Multi Segment Relationships

The primary reason to use overlap columns in a DataFlex environment was to define relationships. Up until DataFlex 11, relationships had to be defined from one single column to one single column. Overlap columns were used to create multi-segment relationships while still complying with the one-column relationship requirement. With the introduction of VDF11, multi-segment relationships are now supported, eliminating the need to define overlap fields for multi-segment relationships.

See Also